A standard stackable storage/transport container has four walls and a floor forming an upwardly open generally parallelepipedal vessel having a rectangular upper rim. A one-piece or two-piece cover is hinged on the rim and can be interlocked with the upper rim of the container by means of a connection in the form of interfitting retaining formations. With a two-piece or two-panel cover, the inner edges of the cover panels are locked together by the retaining formations. In this case the inner edges typically overlay at least partially.
Such containers, generally made of plastic and produced by an injection-molding procedure, with an attachable cover or a cover hinged at one side and interlockable with the upper rim of the container or with a two-piece cover are well known. In the case of a container known from DE 92 12 813 with a cover consisting of two panels, the free inner edges of which overlap along at least one section of a closure line, the overlapping inner edges can be interlocked by means of interfitting retaining formations. These formations include at least one longitudinal ridge and a pocket in the corresponding container rim or panel edge coordinated thereto.
A box or container known from U.S. Pat. No. 4,432,467 has a two-piece cover, with, in a first embodiment, a linear closure line as the two halves of the cover each have one overlapping cover tab and in a different embodiment a wavelike closure line with several overlapping cover tabs. There, the overlapping areas are in any case designed such that in the closed state bars provided at the inner side, transverse side and longitudinal side at the one cover half frame block-like projections at the upper side of the other cover half. These bar-like and block-like fittings are there to restrain a relative side movement when the halves of the cover close the box and when full containers are stacked one upon the other, their weight bears on the container below or the containers below. A further support in the closed state of this box is given by the fact that the corner areas of the halves of the cover overlap as well and interlock due to projections pointing downward in these facing recesses.
The known covers showed, however, that a deformation of the interlocking elements (groove-ridge connection or block interlocking with resistance areas) under heavy load cannot be excluded, the interlocking elements being forced into an inclined position and then sliding over each other and thus the eliminating form-fitting connection. Consequently, the cover, especially a two-piece cover, collapses completely along the closure line, which additionally implicates a risk of injury. As a result, it is important to consider that the containers when stacked one upon the other with their covers closed, have to bear a significant load acting on them, especially on the lower containers. The weight of the load is distributed over the central sections of the cover and the interlocking connection is detached, particularly in the case of two-piece covers.